In a well-known technique, the optical axis direction of a headlight of a vehicle body is controlled in accord with a pitch angle (elevation angle) of the vehicle with respect to a road surface. For the control of the optical axis, the vehicle is provided with an inclination sensor to detect the pitch angle of the vehicle. The optical axis direction is controlled on the basis of a detection value of the sensor (see PTL 1).
Further, in a well-known technique, a vehicle height sensor is provided to either a front wheel or a rear wheel of a vehicle. The detection value of the vehicle height sensor is used as a basis to estimate a displacement angle of the vehicle height on the side of the wheel not provided with the vehicle height sensor. Then, using the estimate value and the detection value of the vehicle height sensor, a pitch angle of the vehicle is calculated. In accord with the calculated pitch angle, the optical axis of the headlight is appropriately controlled (see PTL 2).